A wide variety of window constructions for both original and replacement windows are known in the art. Such windows include single-hung, double-hung and casement window constructions for use in residential as well as other building constructions. Among the older double-hung designs are wood sash window assemblies where the sashes are non-removable and connected by the jambs along the full height of both sides of the sash. Advantages of this system include good wind load resistance and means for providing good air infiltration resistance properties to the window.
However, more modern double-hung window constructions provide for ease of removal of the sash for cleaning purposes and to allow entrance and egress to construction through the window jamb. Such constructions include conventional double-hung tilt sash constructions well-known in the industry. Such windows have the advantage of ease of sash removal. However, in many cares, because each sash is connected to the jamb at four points via the tilt bars at the bottom and two tilt latches at the top, wind load resistance is decreased over non-removable window constructions. Moreover, such window constructions cause greater air infiltration during high wind load conditions. The problem is particularly pronounced in P.V.C. window constructions where overall mechanical strength may be lower than some wood or metal window designs, such as casement constructions. Such P.V.C. window constructions further often have an undesirable plastic look rather than the more acceptable wood grained appearance. A number of overlays and wood surfacing techniques have been devised but such materials do not enhance mechanical strength features in comparison to other constructions.